Three-dimensional routed manifolds with externally inserted cables

Abstract

The Automatic Test Equipment industry must maintain a tester accuracy of roughly one tenth the pulsewidth of the device under test (DUT). Funneling a vast number of electrical signals into a very tiny area to contact the DUT while still maintaining good signal fidelity is a problem not only in the ATE industry, but also for personal computers, network servers and supercomputers. As the speed of processors increase, ATE companies must find new ways to achieve the required accuracy. A solution to this problem is investigated whereby a large number of semi-rigid coaxial wires are routed in 3D space from a low-density array (the tester side) to a high-density array (the DUT side). The three dimensional paths are subject to bend constraints and cannot intersect with any other paths. A software program has been written and tested that is able to find solutions to this 3D routing problem for many test cases. For relatively simple test cases with less than 15 wires, solutions can typically be found in under a minute. Once the geometries of the paths are determined, a block is made with 3D tunnels transversing through it. This part is created using a 3D additive process (e.g. stereolithography), and the coaxial wires are pushed into each tunnel. The maximum force used to insert a wire into a tunnel is limited by the force at which buckling occurs. Uncontrolled buckling of the coaxial wire will compromise electrical signal fidelity or cause opens and must therefore be prevented. To this end, models have been developed to predict the force required to push wires into a predetermined path. Relatively good experimental agreement, within 20% in many cases, was achieved for paths with radii of curvature to wire diameter ratios between 200:1 and 10:1. A perfectly elastic beam model is developed as well as an elastic-plastic beam model.

(cont.) Additional models are developed which account for the friction and the effect of clearance between the tunnel and the beam. The model is used to guide the routing software such that no path is created that cannot have a wire inserted into it. The solution proposed provides an excellent alternative to a printed circuit board for high speed electrical signals. The general method of using additive manufacturing to create tunnels to guide signal opens up many possibilities for not just coaxial cables, but fluid piping, optical fibers and solid wires. The solution has many further advantages and applications that are reviewed briefly but have not been investigated.